A peracetic acid solution is a solution commonly used for disinfection/sterilization in fields such as medicine, and food production. Peracetic acid is an unstable substance that decomposes with time. Consequently, significant changes in the concentration of peracetic acid in a solution can occur, making it necessary to monitor and control its concentration.
One example of a commonly used method for measuring peracetic acid concentration is described in Patent Literature 1. The method described in Patent Literature 1 teaches measuring the concentration of peracetic acid by measuring the amount of change in oxidation reduction potential in the reaction between peracetic acid, contained in a sample solution, and iodide ions, contained in an inter solution of a measuring device. When applying the method described above it is possible to substitute iodide ions with bromide ions.
A second commonly used acid concentration measuring method is described in Patent Literature 2, and involves the use of a membrane covered type sensor. The method described in Patent Literature 2 is primarily used for measuring concentration of hydrogen peroxide, but can also be applied to measuring the concentration of peracetic acid.
The membrane covered type sensor described in Patent Literature 2 includes: a hydrogen peroxide-permeable tubular body; rubber plugs that close up the opposite ends of the tubular body; electrodes (a working electrode and an counter electrode) held in the tubular body; an internal solution; and an enzyme fixing film disposed outside the tubular body.
The membrane covered type sensor described in Patent Literature 2 senses hydrogen peroxide by sensing the strength of an electric current that is generated when hydrogen peroxide in a sample solution comes in contact with the internal solution, and an oxidation-reduction reaction takes place at the electrode surface. Also, in the membrane covered type sensor described in Patent literature 2, silicon rubber superior in flexibility and elasticity is used for the hydrogen peroxide-permeable tubular body.